Prospective validation of the Juvenile Spondyloarthritis Disease Activity Index in children with enthesitis-related arthritis

Objective To measure disease activity in children with enthesitis-related arthritis the Juvenile Spondyloarthritis Disease Activity Index (JSpADA) was developed and retrospectively validated. We prospectively validated JSpADA and also assessed performance of adult SpA scores. Methods Children with enthesitis-related arthritis (ILAR criteria) less than 18 years of age were enrolled. Baseline characteristics and different disease activity measures (JSpADA, BASDAI, Ankylosing Spondylitis Disease Activity Score-ESR, juvenile arthritis DAS-10 joints), and Childhood HAQ, physician global assessment and patient global assessment were recorded at baseline. In some children follow-up was also done. Results The mean (s.d.) age of 127 children (116 boys) was 14.3 (2.4) years and disease duration was 36.9 (3) months. Ninety of 104 (86.5%) children were HLA-B27 positive. JSpADA showed high correlation with physician global assessment (r = 0.87; P < 0.0001), patient global assessment (r = 0.80, P < 0.0001), juvenile arthritis DAS-10 joints (r = 0.89; P < 0.0001) and Childhood HAQ (r = 0.83, P < 0.0001). The JSpADA scores showed good internal consistency, discriminative validity and sensitivity to change. In 15% of children back mobility could not be tested due to active arthritis in lower limbs. The 7-variable JSpADA excluding back mobility performed as well as the original JSpADA. Adult scores showed good construct validity, discriminative capacity and sensitivity to change, and had good correlation with JSpADA (BASDAI, r = 0.84; Ankylosing Spondylitis Disease Activity Score-ESR, r = 0.84). Conclusion JSpADA is a valid score for measuring disease activity in enthesitis-related arthritis. Adult scores also performed well. Excluding back mobility needs to be assessed in future to improve JSpADA performance.